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//
// ofdmflexframesync_example.c
//
// Example demonstrating the OFDM flexible frame synchronizer.
//
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#include <getopt.h>
#include <time.h>
#include "liquid.h"
void usage()
{
printf("ofdmflexframesync_example [options]\n");
printf(" -h : print usage\n");
printf(" -s <snr> : signal-to-noise ratio [dB], default: 20\n");
printf(" -F <freq> : carrier frequency offset, default: 0.002\n");
printf(" -M <num> : number of subcarriers (must be even), default: 64\n");
printf(" -C <len> : cyclic prefix length, default: 16\n");
printf(" -n <len> : payload length [bytes], default: 120\n");
printf(" -m <mod> : modulation scheme (qpsk default)\n");
liquid_print_modulation_schemes();
printf(" -v <crc> : data integrity check: crc32 default\n");
liquid_print_crc_schemes();
printf(" -c <fec> : coding scheme (inner): h74 default\n");
printf(" -k <fec> : coding scheme (outer): none default\n");
liquid_print_fec_schemes();
printf(" -d : enable debugging\n");
}
// callback function
int callback(unsigned char * _header,
int _header_valid,
unsigned char * _payload,
unsigned int _payload_len,
int _payload_valid,
framesyncstats_s _stats,
void * _userdata);
int main(int argc, char*argv[])
{
//srand(time(NULL));
// options
unsigned int M = 64; // number of subcarriers
unsigned int cp_len = 16; // cyclic prefix length
unsigned int taper_len = 4; // taper length
unsigned int payload_len = 120; // length of payload (bytes)
modulation_scheme ms = LIQUID_MODEM_QPSK; // modulation scheme
fec_scheme fec0 = LIQUID_FEC_NONE; // inner code
fec_scheme fec1 = LIQUID_FEC_HAMMING128; // outer code
crc_scheme check = LIQUID_CRC_32; // validity check
float noise_floor = -80.0f; // noise floor [dB]
float SNRdB = 20.0f; // signal-to-noise ratio [dB]
float dphi = 0.02f; // carrier frequency offset
int debug = 0; // enable debugging?
// get options
int dopt;
while((dopt = getopt(argc,argv,"uhds:F:M:C:n:m:v:c:k:")) != EOF){
switch (dopt) {
case 'u':
case 'h': usage(); return 0;
case 'd': debug = 1; break;
case 's': SNRdB = atof(optarg); break;
case 'F': dphi = atof(optarg); break;
case 'M': M = atoi(optarg); break;
case 'C': cp_len = atoi(optarg); break;
case 'n': payload_len = atol(optarg); break;
case 'm': ms = liquid_getopt_str2mod(optarg); break;
case 'v': check = liquid_getopt_str2crc(optarg); break;
case 'c': fec0 = liquid_getopt_str2fec(optarg); break;
case 'k': fec1 = liquid_getopt_str2fec(optarg); break;
default:
exit(-1);
}
}
unsigned int i;
// TODO : validate options
// derived values
unsigned int buf_len = 256;
float complex buf[buf_len]; // time-domain buffer
// allocate memory for header, payload
unsigned char header[8];
unsigned char payload[payload_len];
// create frame generator
ofdmflexframegenprops_s fgprops;
ofdmflexframegenprops_init_default(&fgprops);
fgprops.check = check;
fgprops.fec0 = fec0;
fgprops.fec1 = fec1;
fgprops.mod_scheme = ms;
ofdmflexframegen fg = ofdmflexframegen_create(M, cp_len, taper_len, NULL, &fgprops);
// create frame synchronizer
ofdmflexframesync fs = ofdmflexframesync_create(M, cp_len, taper_len, NULL, callback, (void*)payload);
if (debug)
ofdmflexframesync_debug_enable(fs);
// initialize header/payload and assemble frame
for (i=0; i<8; i++)
header[i] = i & 0xff;
for (i=0; i<payload_len; i++)
payload[i] = rand() & 0xff;
ofdmflexframegen_assemble(fg, header, payload, payload_len);
ofdmflexframegen_print(fg);
ofdmflexframesync_print(fs);
// create channel and add impairments
channel_cccf channel = channel_cccf_create();
channel_cccf_add_awgn(channel, noise_floor, SNRdB);
channel_cccf_add_carrier_offset(channel, dphi, 0.0f);
// generate frame, push through channel
int last_symbol=0;
while (!last_symbol) {
// generate symbol
last_symbol = ofdmflexframegen_write(fg, buf, buf_len);
// apply channel to buffer (in place)
channel_cccf_execute_block(channel, buf, buf_len, buf);
// push samples through synchronizer
ofdmflexframesync_execute(fs, buf, buf_len);
}
// export debugging file
if (debug)
ofdmflexframesync_debug_print(fs, "ofdmflexframesync_debug.m");
ofdmflexframesync_print(fs);
// destroy objects
ofdmflexframegen_destroy(fg);
ofdmflexframesync_destroy(fs);
channel_cccf_destroy(channel);
printf("done.\n");
return 0;
}
// callback function
int callback(unsigned char * _header,
int _header_valid,
unsigned char * _payload,
unsigned int _payload_len,
int _payload_valid,
framesyncstats_s _stats,
void * _userdata)
{
printf("**** callback invoked : rssi = %8.3f dB, evm = %8.3f dB, cfo = %8.5f\n", _stats.rssi, _stats.evm, _stats.cfo);
unsigned int i;
// print header data to standard output
printf(" header rx :");
for (i=0; i<8; i++)
printf(" %.2X", _header[i]);
printf("\n");
// print payload data to standard output
printf(" payload rx :");
for (i=0; i<_payload_len; i++) {
printf(" %.2X", _payload[i]);
if ( ((i+1)%26)==0 && i !=_payload_len-1 )
printf("\n ");
}
printf("\n");
// count errors in received payload and print to standard output
unsigned char * payload_tx = (unsigned char*) _userdata;
unsigned int num_errors = count_bit_errors_array(_payload, payload_tx, _payload_len);
printf(" bit errors : %u / %u\n", num_errors, 8*_payload_len);
return 0;
}
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